While it is not easy for a Cu—Ni—Si-based copper alloy to have all properties of high strength, high conductivity, and excellent bending workability, generally, the Cu—Ni—Si-based copper alloy is excellent in terms of a variety of characteristics, and is inexpensive, and thus is widely used as a conductive member such as a connector for vehicle electric connection or a connection terminal for a print substrate after a plating treatment is carried out on the surface of the copper alloy to improve the electric connection characteristic and the like. Recently, there has been a demand not only for high strength and high conductivity but also for strict bending workability such as 90° bending after notching.
In addition, the connector for electric connection used in the periphery of the recent vehicle engine is required to have excellent durability (stress relaxation resistance or thermal creep properties) against a deterioration phenomenon of the contact pressure decreasing as time elapses to ensure contact reliability in a high-temperature environment.
In addition, it is usual to manufacture the conductive member such as a connector for vehicle electric connection or a connection terminal for a print substrate by pressing copper or a copper alloy, and a steel material such as dies steel or high-speed steel is used for a press mold. A majority of age-hardenable copper-based alloys such as a Cu—Ni—Si-based copper alloy contain an active element and have a tendency of significantly abrading a press mold compared with generally used phosphor bronze. When a press mold is abraded, burrs or shear drops are generated on a cross-sectional surface of a material to be worked, the deterioration of a worked shape is caused, and the manufacturing cost rises, and thus there is another demand for a Cu—Ni—Si-based copper alloy having excellent mold abrasion resistance and shear workability (press punching properties).
To solve the above-described problems, PTL 1 discloses a copper alloy having excellent press workability in which (1) composition: an element having an oxide standard free energy of formation of −50 kJ/mol or less at room temperature is used as an essential additive element, the content thereof is in a range of 0.1 mass % to 5.0 mass %, the remainder is Cu and inevitable impurities, (2) layer structure: a Cu layer having a thickness in a range of 0.05 μm to 2.00 μm is provided, and the compressive residual stress is 50 N/mm2 or less at a point 1 μm inside from the interface between the Cu layer and a copper-based alloy.
PTL 2 discloses a Corson-based copper alloy sheet in which, when a copper alloy rolled sheet made of a Cu—Ni—Si-based copper alloy is finishing-cold-rolled, the finishing cold rolling is carried out at a working rate of 95% or more before a final solution treatment, the finishing cold rolling is carried out at a working rate of 20% or less after the final solution treatment, then, an aging treatment is carried out so that the average crystal grain diameter in the copper alloy sheet reaches 10 μm or less, the copper alloy sheet has a texture in which the proportion of Cube orientation {001}<100> is 50% or more in the measurement result of an SEM-EBSP method, the copper alloy sheet structure has no lamellar boundary that can be observed in a structure observation using a 300-time optical microscope, the strength is high so as to have a tensile strength of 700 MPa or more, the bending workability is excellent, and the conductivity is also high.
PTL 3 discloses a material for an electronic component which suppresses mold abrasion and has excellent press punching properties in which a copper-based alloy base material containing 0.1 mass % to 5.0 mass % of an element having an oxide standard free energy of formation of −42 kJ/mol or less at 25° C. is coated with a Cu layer in which the total content of components other than S≤500 ppm, 0.5≤S≤50 ppm, the purity of Cu≥99.90%, and the thickness is in a range of 0.05 μm to 2.0 μm.
PTL 4 discloses a Cu—Ni—Si-based copper alloy sheet material having a composition including 0.7 mass % to 4.0 mass % of Ni and 0.2 mass % to 1.5 mass % of Si with a remainder of Cu and inevitable impurities, in which, when the X-ray diffraction intensity of a {200} crystal plane on the sheet surface is represented by I{200}, and the X-ray diffraction intensity of a {200} crystal plane of standard pure copper powder is represented by I0{200}, the crystal orientation satisfies I{200}/I0{200}≥1.0, when the X-ray diffraction intensity of a {422} crystal plane on the sheet surface is represented by I{422}, the crystal orientation satisfies I{200}/I{422}≥15, a high strength of a tensile strength of 700 MPa or more is held, the anisotropy is small, the bending workability is excellent, and the stress relaxation resistance is excellent, and a method for manufacturing the same.